1. Field of the Invention
The present invention relates to the field of gas turbines. It relates to an emission probe for the removal of exhaust gas from the combustion chamber of a gas turbine, comprising a one-piece probe tube which, in its interior, has an emission passage extending in the direction of the tube axis and two cooling passages extending parallel to the emission passage and adjacent to one another.
An emission probe of this kind has already been used in practice.
2. Discussion of Background
Emission or exhaust-gas probes are used in the case of combustion processes wherever it is necessary to determine and monitor the effectiveness of the combustion process itself and the pollutant content of the exhaust gases. Problems arise here, in particular, from the generally high exhaust-gas temperatures, which in the case of gas turbines, for example, can be well above 1000.degree. C. and, on the one hand, stress the probe itself and, on the other hand, can alter in an undesirable manner the exhaust-gas samples removed (e.g. due to secondary chemical reactions).
Patent Specification GB-B-1 557 970 has already disclosed an exhaust-gas probe for a gas turbine which is constructed from a plurality of tubes situated one inside the other, the inner gas removal tube being surrounded by a plurality of concentrically arranged cooling passages. The known exhaust-gas probe is of very complex construction because different individual tubes have to be assembled in a manner which will withstand the high operating temperatures, At the same time, this manner of construction makes integration into existing components of the gas turbine more difficult.
An emission probe of simpler construction, as depicted in cross section in FIG. 1, has furthermore been used in practice. The emission probe 11 comprises a one-piece probe tube 12 in which an emission passage 13 and two cooling passages 14a, b of approximately the same cross section are arranged parallel to the tube axis at the corners of an isosceles triangle. For the purpose of removing samples, the emission passage 13 is connected by removal holes 15 to the external space of the probe. The probe is installed with its axis transverse to the flow of exhaust gas, with the result that the exhaust gas flows around the probe. The probe is oriented in such a way that the outer openings of the removal holes 15 lie directly at the stagnation point of the flow. The direction of flow is indicated in FIG. 1 (as also in FIG. 2b) by a vertical arrow.
Probes of this kind have already been used under high pressure in combustion-chamber tests, but the cooling was insufficient for the requirements because the cooling passages comprised cylindrical longitudinal holes. As a result, the cooling effect was limited and the zones which were furthest away from the cooling passages were rapidly overheated. This applies particularly to the portion at the stagnation point where the holes for exhaust-gas removal are situated. A further disadvantage of the old design is the fact that the probes are permanently warped by differential thermal expansions.